The performance of LASIK (laser in situ keratomileusis) surgery is typically accompanied by the cutting of a thin flap in the cornea, which is then lifted and folded back along a hinge to expose the corneal stroma beneath. An ablating laser is used to perform refractive surgery, and the flap is replaced.
Several methods have been used to avoid or detect any “wrinkles,” or striae, in the corneal flap after replacement atop the stroma. For example, the cornea can be marked prior to cutting so that the markings can be used to realign the flap. Another method employs the operating (direct-view) microscope and a diffuse, broadband, white light source to detect striae. Alternatively, the refractive surgeon may use a dedicated apparatus, such as a handheld slit lamp, to project a thin line of visible broadband, white light onto the cornea to scan for surface aberrations or edges.
However, the flooding of the eye with such illumination to detect flap position, debris, and hydration can be uncomfortable for the patient, and the use of a slit lamp to detect flap replacement and general eye condition can compromise work flow. Further, white light may not provide optimal enhancement of parts of the eye for visualization. To view at alternate wavelengths, external camera systems with standard video monitors can be used, but, in order to eliminate the high illuminations required for direct-view microscopes, larger apertures must be used, mandating a tradeoff between patient safety and doctor view.